The present invention relates to a document feeding apparatus and an image reading apparatus, which are employed for a copier, a facsimile, a scanner, etc.
Referring to FIG. 1, operations performed in the conventional document feeding apparatus will be detailed in the following. Incidentally, although FIG. 1 shows a mechanical configuration of the document feeding apparatus embodied in the present invention, contents of operations to be performed in the document feeding apparatus of the present invention are different from those performed in the conventional document feeding apparatus, as described later.
As shown in FIG. 1, a forwarding roller 2 forwards documents D stacked on a document feeding tray 1, and a document feeding roller 4 separates the documents D to feed a single sheet of the documents D. After the separated single sheet of the documents D is temporally stopped at a registration roller 6, the sheet of documents D passes through a document reading position 7 while being conveyed by the registration roller 6, and finally is ejected onto an ejecting tray 8.
In the forwarding operation performed by the forwarding roller 2, a document pushing plate 3 elevates upward to push the documents D against the forwarding roller 2. Further, at a separating position where a single document is separated from the documents D, the document feeding roller 4 rotates while press-contacting a separating roller 5 so as to separate the single document from the documents D.
In a continuous conveying operation for continuously conveying a plural sheets of documents D, the forwarding roller 2, the document pushing plate 3, the document feeding roller 4 and the registration roller 6 are not continuously operated, but are intermittently operated in repetitions between activation and deactivation for every feeding operation of a single sheet of the documents D (hereinafter, the term of “document D” represents a single sheet of documents D, while the term of “documents D” represents a plurality of documents as one group).
Concretely speaking, the rotation of the forwarding roller 2, the elevation of the document pushing plate 3 and the rotation of the document feeding roller 4 are activated substantially at a same time to forward the document D. Then, after a short time period has passed since the leading edge of the document D detected by the sensor S4 disposed immediately in front of the registration roller 6, the forwarding roller 2 and the document feeding roller 4 are deactivated, and, after a loop of the document D is formed between the document feeding roller 4 and the registration roller 6, the registration roller 6 is activated to convey the document D. At the same time when the forwarding roller 2 and the document feeding roller 4 are deactivated, the document pushing plate 3 is activated to descend. The driving action of the registration roller 6 is deactivated after a predetermined time period has passed, and, after its driving action is deactivated, the registration roller 6 is driven by the passing action of the document D to rotate. While the registration roller 6 is activated, the forwarding roller 2 and the document feeding roller 4 are idle running due to an action of a one-way clutch mechanism.
The abovementioned operations performed between the forwarding roller 2 and the registration roller 6 are repeated for every document D. Further, the activating timing of the forwarding roller 2, the document pushing plate 3 and the document feeding roller 4 is set at a time interval determined in advance corresponding to a document size. Incidentally, information in regard to the document size are acquired, based on the detection results detected by document sensors S1-S3 mounted on the document feeding tray 1 and a document width detector (not shown in the drawings), which detects positions of the regulating members for regulating the position of the document D in the width direction.
In such the operation for controlling the document feeding apparatus, the deactivation control, for prohibiting the feeding action after detecting the final document by detecting a final single sheet of documents D residing on the document feeding tray 1, is conducted on the basis of the document absence detection signals detected by the document sensors S1-S3 serving as a document detector. The document absence detecting operation to be performed by document sensors S1-S3 is achieved in such a manner that the document sensors S1-S3 detect the fact that none of documents D reside on upper side of the document sensors S1-S3. This is achieved when the trailing edge of the final document D passes through any one of the document sensors S1-S3, which is detecting the trailing edge of the final document D at a position being farthest from the forwarding roller 2.
Patent Document 1 sets forth a configuration in which a plurality of document detectors are provided so as to select and use one of the plurality of document detectors. According to the invention set forth in Patent Document 1, the final document detecting operation is surely performed in the small-sized document feeding apparatus.
[Patent Document 1]                Japanese Patent No.3404708        
In such the document conveyance controlling operation, the final document D is forwarded after the final document D is detected. Incidentally, although the final document D is detected by the document sensors S1-S3 mounted on the document feeding tray 1, it is impossible for the document sensors S1-S3 to detect the final document D when the documents D are small-sized to such a extent that the document sensors S1-S3 cannot detect. Accordingly, when detecting the final document D of such the small-sized documents D, a document sensor S5 disposed at a position near the forwarding roller 2 is employed for detecting whether or not the document D resides on the document feeding tray 1.
Each of the document sensors S1-S3 is disposed at such a position that is located in the vicinity of a trailing edge of the documents D of each size. Accordingly, any one of document sensors S1-S3 can detect the absence of the next document D just after the final document D started to be fed.
However, the document sensor S5 is not disposed at a position in the vicinity of a trailing edge of the documents D, but at a position near the forwarding roller 2. Accordingly, since it takes some time that the trailing edge of the final document D arrives at the position of the document sensor S5 after the final document D starts to be fed, the detection timing of the final document D to be detected by the document sensor S5 would be delayed.
In the document continuously-conveying mode in which a plurality of documents D are sequentially conveyed one by one, each of documents D is forwarded after confirming that a document D preceding to another document D to be currently forwarded is not the final document D. Therefore, the abovementioned delay of the timing for detecting the final document D causes another delay of the timing for confirming that the current document D is not the final one, resulting in an increase of a time interval for feeding each of the documents D (hereinafter, referred to as a document interval, for simplicity) in the document continuously-conveying mode.
Basically, the document interval in the document continuously-conveying mode is established by considering the relationship with the image reading velocity and the prevention of the jam caused by collisions between documents conveyed before and after, so that the reading efficiency is designed to be raised by shortening the document interval as short as possible. However, due to the aforementioned specific circumstances in the case of the small-sized documents D, there has been a problem for the small-sized documents D that the reading efficiency is lowered since the document interval becomes long.
In the image forming apparatus equipped with the document feeding apparatus, such as a copier, the smaller the image size becomes, the shorter the image forming interval should be, so as to efficiently perform the image forming operation. Accordingly, in the document feeding apparatus, the deterioration of the conveying efficiency in the case of the small-sized documents D causes a mismatch with the image forming efficiency in the image forming section, and therefore, the abovementioned problem becomes a practical obstacle.
Concretely speaking, despite that the image forming section has a capability of forming image in a higher efficient mode, the image forming section is obliged to lower the image forming efficiency so as to match it with the deterioration of the conveying efficiency.